Evidence from children's performance in a variety of tasks suggests a change in the kinds of similarities children notice and use. Children tend to focus on literal similarity and then shift to the use of common objects, followed by common relations between objects, and finally relations between relations. Research from a variety of different domains and tasks supports this "career of similarity," and the shift in similarity use appears to be learning based, not maturational, since it occurs at different ages in different domains. Finally, it seems that two processes act to change the representations within a domain so that relations come to be represented more uniformly within the domain. These processes are: (1) carrying out other similarity comparisons in which the alignment of two representations promotes further commonalities; and (2) learning and applying relational labels. (Five figures, and 26 notes are included; 151 references are attached.) (Author/PRA)